The overall objectives for this research are as follows: (1) to clarify further the regulatory mechanisms of human natural killer (NK) cells; (2) to develop methods to identify the cellular components of these regulatory pathways and study their interrelationships in various disease states in order to learn about the significance of the NK system in the etiology and control of such diseases; (3) to study the mechanism of killing mediated by the NK cells; (4) to perform comparative studies in various animal species on the role of the large granular lymphocyte (LGL) shown to be the mediator of NK activity in humans.